EXCHANGE
BULLETIN OF
PURDUE UNIVERSITY
PUBLICATIONS OF THE ENGINEERING DEPARTMENTS
VOL. VI OCTOBER 1922 NO. 2
15
Fundamentals of Construction
and Maintenance of
Secondary Type Highways
By
CHARLES C. ALBRIGHT
BULLETIN NO. 1
ENGINEERING EXTENSION SERVICE
^ -LXFAYETTE, INDIANA
Published by Purdue University at LaFayette, Indiana
Entered at the Post Office at LaFayette as second class matter under
the Act of July 16, 1894.
THE ENGINEERING EXTENSION SERVICE
OF
PURDUE UNIVERSITY
Purdue University recognizes its opportunity for public
service by carrying the benefits of its teaching and research
activities to those in the State who are interested in engineering
problems, but who are unable to be benefited by the regular
courses of resident instruction which are offered at the Uni-
versity.
The Engineering Extension Service of Purdue University is
carried on in the following ways :
1. Conferences are held at Purdue University and at other
places in Indiana for the benefit of road builders, canners, elec-
trical workers, power plant men, foundrymen and for others
engaged in manufacturing and in public utility industries.
2. Groups of lectures are delivered by engineering experts
of Purdue University for the benefit of industrial workers and
executives. Talks are also given on subjects related to engineer-
ing before civic, commercial and manufacturing organizatio;
3. Publications in the form of bulletins and circulars are
issued containing up-to-date information on engineering subjects.
Address communications concerning Engineering Extension
Service to
DIRECTOR OF ENGINEERING EXTENSION SERVICE,
Purdue University, Lafayette, Indiana.
BULLETIN NO. 1
ENGINEERING EXTENSION SERVICE
Fundamentals of Construction
and Maintenance of
Secondary Type Highways
By
CHARLES C. ALBRIGHT
Professor of Railway Civil Engineering
In Charge of Highway Engineering
PURDUE UNIVERSITY
LAFAYETTE, INDIANA
OCTOBER, 1922
Tfij
Civil l-:iii;iii;MTiii;
CONTENTS
Page
CHAPTER I. Introduction ....'. . 5
CHAPTER II. Elements of Road Construction 7
CHAPTER III. Elements of Earth Road Maintenance 13
CHAPTER IV. Construction of Sand-Clay, Cinder and Shale Roads 18
CHAPTER V. Maintenance of Sand-Clay, Cinder and Shale Roads 21
CHAPTER VI. Gravel Road Construction 21
CHAPTER VII. Gravel Road Maintenance 25
CHAPTER VIII. Macadam Road Construction 27
CHAPTER IX. Macadam Road Maintenance 31
CHAPTER X. Dust Prevention 32
CHAPTER XL Bituminous Carpets 35
ILLUSTRATIONS
Page
Frontispiece Civil Engineering Building.
Fig. 1. Cross-section of an Earth Road 8
Fig. 2. Determining Crown with Level Board .'.. 8
Fig. 3. Shaping Earth Subgrade and Side Ditches with Blade Grader 9
Fig. 4. Washout along Hillside Road 10
Fig. 5. Lowering Ground Water with Tile Drains 10
Fig. 6. False Ditch between Roadway and Berm 11
Fig. 7. A Good Sign to Follow, Allen County 11
Fig. 8. A Good Highway with Flat Curves and Light Grades 12
Fig. 9. Details of a Plank Drag 14
Fig. 10. An Earth Road before Improving 15
Fig. 11. An Earth Road after Improving 15
Fig. 12. Small Culvert Clogged with Weeds 16
Fig. 13. Water Held in Side Ditches Softens the Subgrade 16
Fig. 14. An Earth Road in Poor Condition 17
Fig. 15. Improperly Drained and Shaped Road on Steep Hill 18
Fig. 16. Clay Hill with Sand Spread and Harrowed 19
Fig. 17. Hill with Consolidated Sand-Clay Surface 19
Fig. 18. Washed Gravel for Road Construction < 21
Fig. 19. A Poorly Constructed Gravel Road 23
Fig. 20. A Good Gravel Road 23
Fig. 21. Poor Drainage and Insufficient Depth of Surface Material
Caused this Gravel Road to Break Up 24
Fig. 22. Dangerous Point on Road Caused by Short Culvert 26
Fig. 23. Safe Road with Extended Culvert 26
Fig. 24. Suggested Cross-section of a Macadam Road 28
Fig. 25. Sprinkling Macadam Prior to Last Rolling 29
Fig. 26. A Properly Shaped and Maintained Macadam Road 30
Fig. 27. Crushed Stone for Maintenance Along Highway 31
Fig. 28. Spreading a Thin Covering of New Material with Truck 32
Fig. 29. Oiling a Macadam Surface to Prevent Dust 33
Fig. 30. Spreading Cover Material on a Bituminous Carpet 35
Fig. 31. A Bituminous Surface That Has Been Neglected 36
Fig. 32. A Good Bituminous Surface Highway 36
PREFACE
This bulletin of information is prepared in order to bring
the best practice in road work to the attention of the county
and township road officials of Indiana. It is also believed that
city street commissioners, highway contractors and others in-
terested in road problems may find herein material of value to
them. This is not intended to be a complete treatise of the sub-
jects of road building and maintenance under all conditions, but
it is an explanation of the fundamental problems particularly ap-
plicable to Indiana.
A portion of the information in this volume has appeared
in newspaper articles and in mimeograph form.
Special credit is due B. H. Petty, Assistant Professor of
Highway Engineering, for constructive criticism in the prepara-
tion of the manuscript.
September, 1922. C. C. ALBRIGHT.
FUNDAMENTALS OF CONSTRUCTION
AND MAINTENANCE OF
SECONDARY TYPE HIGHWAYS
CHAPTER I
INTRODUCTION
In recent years the improvement of the highways has come
to be one of the most important problems of the times. The
daily press and the technical publications have contained much
discussion about the development of the so-called higher types
of highways. This is important and desirable since less than
10 percent of the rural highways will probably carry 85 percent
of the total traffic. Notwithstanding this fact, 90 per cent of
the highway mileage must carry the remaining 15 percent of
the traffic to and from the individual rural dweller and these
secondary roads are absolute esssentials as connecting links be-
tween the more or less remote rural home and the main high-
ways. The health, happiness, contentment, advancement and
prosperity of those who dwell in the country are largely depend-
ent upon transportation over these roads which are frequently
impassable for periods varying from a few days to several
months per year.
In view of these conditions it appears that too little stress
has been placed on the development of the simple types of roads.
Heavy expenditure of money is not warranted for light traffic,
but it is possible to construct roads of a type that, will answer
practically all the purposes of light traffic for a fraction of the
cost of a hard surfaced road.
The 1914 statistics of the United States Bureau of Public
Roads gave a total of 2,445,760 miles of road in the United States.
Of this amount 257,291 miles, or 10.5 percent, had improved sur-
faces. The statistics of 1919, the latest available, show a cor-
responding total mileage of 2,478,552 with 299,135 miles, or 12.1
percent, improved. The average improvement rate in this period
is, therefore, only three-tenths of one percent per year. This
period was during the World War when little work not absolutely
essential was performed. At the present time the rate of prog-
ress is probably double the above, but the actual construction and
maintenance must be further increased to meet the traffic de-
mands. To illustrate these conditions the following figures are
given : The total production of all kinds of motor vehicles in-
creased from 25,000 in 1905 to over 2,000,000 in 1920 while the
registration of motor vehicles increased from 1,009,513 in 1912
to 9,750,000 in 1921. It will thus be seen that the production of
vehicles increased 8000 percent in 16 years and the registration
increased 900 percent in 10 years. Leading highway engineers
and traffic experts have estimated the desirable rate of increase
in highway improvement to accomodate the traffic demands as
one percent and that this rate is desirable for the next ten or
fifteen years. In 1921 about $420,000,000 were expended for new
construction and $180,000,000 for maintenance, but to meet the
desirable increase of improvement over $1,000,000,000 would be
necessary per year. This places highway work as one of the
leading industries of America and the huge sum of money in-
volved indicates the desirability of expert knowledge on the
subject.
Much study has been given to the road surface, but the sub-
grade factors have been largely neglected. The latter conditions
as well as the surface are now receiving intensive study at the
Bates Experimental Road in Illinois under the direction of the
Illinois Department of Roads and the United States Bureau of
Public Roads. Other tests of importance are being conducted
at Pittsburg, California, and Arlington, Virginia. The data ob-
tained from these experiments with that secured from numerous
others of less importance will be of great value in future high-
way plans.
It seems almost unnecessary today to demonstrate the neces-
sity of road improvement, however, a simple problem in elemen-
tary highway economics may be of some value. The tractive
force required to pull a load on a common farm wagon over un-
improved earth roads is 100 to 300 pounds per ton of load. The
average is 200 pounds per ton. It has been demonstrated that
this can easily be reduced to one-half the value on a properly con-
structed and maintained surface. An estimate for the value of
this improvement, as given by the United States Bureau of Pub-
lic Roads, is 2 to 10 cents per ton mile. The average is 6 cents.
Assume a traffic so light that only ten tons per mile per day is
averaged for 300 days per year. The saving is 300x10x6 or $180
per mile per year. This sum is sufficient to maintain an earth
road in excellent condition for twenty times the assumed tarffic.
$180 also represents the interest at 6 percent on $3000. There-
fore this would justify an expenditure of $3000 per mile for
permanent improvement, i. e., grading, drainage, culverts, bridges,
guard fences, signs, etc. The cost of grading the average road
in a suitable manner for present or future permanent improve-
ment will be $1,000 to $4,000 per mile.
Since the motor vehicle is found in all rural communities and
predominates in many, this discussion would not be complete
without some reference to the economies of motor transport.
There is very little reliable data available concerning the
cost of motor traffic ; but in 1918 some valuable tests were con-
ducted in the vicinity of Cleveland, Ohio. These experiments
dealt entirely with the fuel consumption of trucks running over
various road surfaces. The gasoline consumed on gravel and
macadam roads was 60 to 80 percent of that on earth roads ;
while on the best type of brick and concrete roads it was only
50 percent. On a basis of fuel alone the gravel road would give
a saving, at 23 cents per gallon, of 1.4 cents per mile. In addi-
tion the better classes of roads offer a saving in time of travel,
repairs, wear on tires, oils, other lubricants and depreciation.
Assuming a daily tarffic of 20 trucks per mile for 300 days,
we have a yearly saving per mile on the gravel road of 300x20x
$0.014 or $84. This is 6 percent on a capital charge of $1,400.
It has been stated that the results of these tests were largely
responsible for the success of a $60,000,000 bond issue for hard
surfaced roads in Illinois.
First class gravel and macadam roads with 18 foot wearing
surfaces, exclusive of sub-grade and structures, capable of carry-
ing several hundred average vehicles per day can be constructed
for $8,000 to $14,000 per mile. The total cost in any individual
case will vary with many local factors.
CHAPTER II
ELEMENTS OF ROAD CONSTRUCTION
At the present time the public roads of Indiana have been
largely laid out or as commonly stated have been constructed.
On many of the secondary roads the latter word is greatly mis-
leading as practically no construction work has been done other
than plowing a shallow side ditch and scraping some of the sod
and surface material to the center of the road. Indiana has
84,400 miles of rural highways, about 35,000 miles of which have
been surfaced. Of the total mileage 50,000 have no surface ma-
terial other than the local soil. Little or no attention has been
paid to adequate grading, drainage or improving much of this and
in wet weather these roads are continuous mud holes while in
dry weather they are rough and dusty trails.
Construction and maintenance both vary with soil condi-
tions. Typical soils of Indiana are the heavy clays of the Mau-
mee Valley, the light shifting sands of the Dunes region along
lake Michigan, the gravel and sandy loams of the north central
region, the black soil near a part of the Illinois line, the clays of
the southern Knobs and the silts of the lower Wabash and Ohio
River Valleys.
Proper drainage is the essential basis of all highway im-
provement. No road can be properly built or kept in good con-
dition unless provision is made for the elimination of all free or
8
excess water. In the sandy soils previously mentioned this is
easily accomplished, but particular care must be taken in order to
secure favorable results with clay or gumbo soils. If the soil is a
light, fine sand, a flat crown and shallow side ditches will usu-
ally suffice. The sand will have less tendency, under these condi-
tions, to shift or drift. Any rain except the very heaviest will be
rapidly absorbed by the sand or quickly carried away by the
shallow ditches.
/7/se /e C
Fig. 1. Cross-section of an earth road.
Fig. 2. Determining crown with level board.
In a clay or dense soil the side ditches should generally be
eighteen inches or more below the crown of the road. This will
vary with the steepness of the grade across and parallel to the
road, the width of the road and the average intensity of the
rainfall. The ditch section may be V shaped or flat bottomed.
The former shape is gaining favor as it can both be constructed
and maintained with the common road grader or scarper which
reduces the labor cost. If a flat bottom is used it should not be
less than 24 to 30 inches in width so that a slip or drag scraper
can be used for construction and cleaning purposes.
Water should be taken from the side ditches at frequent
intervals and carried away in natural drainage channels to pre-
vent danger of "washouts" along the side of the road from the
larger volume of water. It will also be necessary to enlarge the
ditch section if water is to be carried more than 150 to 200 yards.
Fig. 3. Shaping: earth subgrrade and side ditches with blade grader.
When the road is located on a steep hillside, it is often desir-
able to put tile drains on the upper side of the road to intercept
ground water flow. The tile should be placed from 30 to 60
inches below the surface of the ground and always below the
frost line. The trench should be back-filled with gravel or
crushed stone. At the present time some engineers do not be-
lieve such drains are of any value in heavy dense soils. There
can be no question, however, as to their value in intercepting
ground water and lowering the water table under the road in
porous soils. In all cases rainfall and free water should be car-
ried from the travelled way as quickly as conditions will permit.
This applies equally to hard surfaced and to inferior types of
roads. Wet spots in the road can be drained by running a line
of small tile, not less than 4 inch, to the side ditch. If good
coarse gravel or crushed stone is available, a French or blind
drain can be used. This is constructed by digging a narrow
trench and back-filling with coarse aggregate. The grade of
these drains should be not less than one inch in five feet and
the top should be covered with at least six inches of compact soil
in order to prevent rapid clogging of the aggregate. These drains
are quite effective and are often much cheaper than the tile drain.
10
The only purpose in crowning a roadway is to carry surface
water quickly to the side ditches. Too much crown is objection-
able to traffic and will cause vehicles to travel in the same line
at the center of the road. This results in ruts, increases the
danger of collision of passing vehicles and causes loose surface
material to roll to the side of the road. A flat surface would be
the ideal condition as the vehicles would travel over the entire
surface causing uniform wear with less danger of collision and
little displacement of material.
Fig. 4. Washout along hillside road.
Fig 5. Lowering ground water with tile drains.
The crown of a road in heavy soil should be from one-half
to one inch per foot and should seldom exceed three-fourths of
an inch per foot. Thus for a sixteen foot roadway the crown
would be 24x8 or 6 inches. The crown should be carried as a
11
smooth surface to the ditch line. An inferior road will invariably
result if a false ditch is formed .between the roadway and the
berm or shoulder.
Fig. 6. False ditch between roadway and berm.
The width and grade of a road are also important factors.
It is usually advisable on main roads to have the traveled way
wide enough for two vehicles to pass. This together with a
low crown will result in a more even distribution of traffic, will
Fig. 7. A good sign to follow, Allen County,
12
lessen the maintenance work and contributes to the safety of
travel over the road. The total width of the road should include
the traveled way, the shoulders, the side ditches and at least a
narrow berm between the ditch and adjacent property line. The
latter is necessary for the protection of the property line fence.
The shoulders protect both the roadway and the ditch and under
normal weather conditions, when necessary, will carry passing
vehicles. A sure indication that the traveled way is too narrow
is that the maintenance of the shoulders is excessive because of
use by vehicles. Frequent traffic accidents may also indicate
the same thing.
The longitudinal grade of all roads should be as flat as pos-
sible without excessive cost. A rise of one foot in a distance of
one hundred feet adds twenty pounds to the tractive force re-
quired to move a ton of load. A rise of five feet in a hundred
foot distance, therefore, doubles the force required to move this
load on a well graded and maintained earth road. The effect of
grade is more serious in the case of a slow moving animal drawn
load than for a motor vehicle moving at higher speeds. The
momentum of the rapidly moving motor vehicle is of material
assistance in overcoming the grade while this factor is practically
negligible in a horse drawn vehicle. For motor traffic short,
straight grades of a maximum of ten percent may be used, but are
not desirable as the maximum safe speed on descending prob-
ably would be exceeded. On sharp curves or on long tangents
the grades should be kept within three to five percent where
possible.
Fig. 8. A good highway with flat curves and light grades.
Short or sharp curves in the alignment of the road should
be avoided as they are a source of danger to passing vehicles.
On main line highways curves should seldom have a radius of
13
less than 300 to 500 feet. Obstructions to sight such as trees
or high banks on the inside of curves should be removed when-
ever possible. There should be a clear view across the inside
of the curve for at least fifty yards on secondary roads and one
hundred yards on main traveled highways.
The methods of construction described in this chapter could
be easily applied, without excessive cost, on a majority of the
highways of Indiana. The funds required for the work would
yield large dividends as the general character and appearance of
the roads would be improved from twenty-five to one hundred
percent, the work of maintenance would be reduced, the cost of
transportation would be lowered and the pleasure of the passing
traveler would be greatly increased.
CHAPTER III
ELEMENTS OF EARTH ROAD MAINTENANCE
Assuming that the sub-grade of a road has been properly
constructed, shaped and drained the next step is the actual main-
tenance of the surface. Weather and traffic iDoth tend to destroy
the finished road and these influences must be met with proper
maintenance. There are normally two main periods of intensive
maintenance, viz., in the early spring just after the frost has
left the ground and in the late autumn just before the final
"freeze up." Immediately after the frost has left the ground is
the best time to use the grader. This should be used to form a
new well defined ditch. At this time also extra material should
be moved to the road surface in order to fill ruts and depressions.
While the road is soft and moist this new material will unite with
the original road top to form a new surface. All sod and loam
or decayed vegetable matter should be removed from the road,
as otherwise it forms a prospective point of failure. This ma-
terial can be used to fill low places along the road or hauled to
adjoining farms as a fertilizer. No loose material should be
placed on the road surface after it has become thoroughly dry
and settled. Loose earth will not unite with the hard top of the
road, but will be stirred up as dust by the vehicles in dry weather
and will form a slop after a rain. The only excuse for adding
loose earth in the summer is because of a washout or other
emergency repair.
The next step is to grade and shape the surface that has
been eroded and scarred by the action of weather and vehicles
during the winter. This can first be accomplished by the steel
bladed grader. The formation of a false ditch at the edge of the
traveled way should be prevented by occasionally passing the
grader or planer over the edge of the shoulder. Good sod is a
material aid in maintaining the shoulders. It also holds loose
14
15
material washed from the surface of the road and may in time
build up the shoulder higher than the road surface. When this
condition occurs the sod must be cut off with the blade grader
or small ditches opened up at frequent intervals across the
shoulders, so that water falling on the surface of the road will be
carried quickly to the side ditches.
Figr. 10. An earth road before improving.
Fig. 11. An earth road after improving,
After the initial grading the road grader, drag or planer
should be used after every rain that is sufficiently heavy to soften
the surface thoroughly. The drag and planer are very inex-
pensive pieces of equipment and are very effective for the minor
work of maintenance during the greater part of the working
16
season. If they are properly used a continual improvement of
the road surface during the season will be effected. By the
intelligent use of simple road machinery it is possible, under fa-
vorable conditions, to produce a surface that will rival for
smoothness a city boulevard. This condition can be maintained
until freezing begins. Certain faults in the road, as wet spots
due to springs or to excessive shade, bad material, etc., should
be studied as they appear and properly corrected.
Fig. 12. Small culvert clogged with weeds.
Fig. 13. Water held in side ditches softens the subgrade.
1?
To secure the best drainage conditions, weeds, high grass
and brush along the shoulders and in the side ditches should be
cut and burned as often as necessary. The frequency of this
work will depend upon the weather and local conditions, but
usually once or twice a year is sufficient. Small culverts and
bridge openings should be cleaned as often as necessary to insure
unobstructed waterways.
Fig:. 14. An earth road in poor condition.
When freezing begins in the autumn the surface will break
up under heavy traffic unless the road has practically perfect
drainage. No earth road will safely carry any but the lightest
traffic during a prolonged rainy season or during alternate freez-
ing and thawing of the ground. At this time the road should
again receive particular attention. Advantage should be taken
of days when the frost is out of the ground to go over the road
with the blade grader or preferably the drag or planer and smooth
out the ruts and wheel tracks. Free water from rainfall and
melting snow will quickly drain from the smooth crowned sur-
face while if held in rough spots it will be absorbed by the road.
In the latter instance mud holes will rapidly develop under traffic
and the road may become impassable. If the road freezes with
a smooth surface it will be agreeable for traffic and will go
through the winter with a minimum amount of damage.
The main points of earth road maintenance may thus be
briefly summarized and are sufficiently important to be placed
18
in the note book of every one who has anything to do with the
work of highway maintenance.
1. Poperly drain the road.
2. Properly shape the road.
3. Use the flattest permissible crown.
4. Prevent the formation of false ditches.
5. Do heavy grading only in early spring.
6. Remove all pockets of inferior material from road
surface.
7. Use grader, drag or planer after all hard or prolonged
rainfall and at such other times as necessary.
8. Patrol road as often as necessary and correct specific
faults as soon as they appear.
9. Keep ditches and culverts free from obstructions.
10. Grade road surface immediately before the winter
"freeze up."
11. During winter weather take advantage of mild, warm
days to smooth out ruts and wheel tracks.
12. Be vigilant at all times and remember the homely
maxim, "An ounce of prevention is worth a pound of
cure."
CHAPTER IV
CONSTRUCTION OF SAND-CLAY, CINDER AND SHALE
ROADS
Sand-clay roads are the next higher type of development
above natural earth. They are satisfactory for a moderate
traffic of animal drawn vehicles and a light traffic of automobiles.
They may be satisfactory for a light traffic of heavy trucks
where the sub-grade is sand, but are seldom satisfactory where
the sub-grade is clay.
Fig. 15. Improperly drained and shaped road on steep hill.
19
The road surface should be shaped and graded as indicated
in a previous chapter. A light crown should be used. If the soil
is sand about two inches of clay should be added in one applica-
tion. These should then be thoroughly mixed, using a disc or
spike tooth harrow. The object is to mix the materials so com-
pletely that the particles of sand and clay are uniformly distrib-
uted. If this is not accomplished certain parts of the surface
will become muddy and rutted in wet weather while other parts
will be loose and sandy in dry weather.
Fig:. 16. Clay hill with sand spread and harrowed.
Fig. 17. Hill with consolidated sand-clay surface.
Where a clay soil is found it should be shaped as before de-
scribed. The surface is then plowed or scarified to a depth of
two or three inches and the clay pulverized by rolling, discing
20
or harrowing. About three or four inches of sand should then
be applied and mixed with the clay after which two or three
inches of additional sand should be applied and thoroughly
mixed. It might be possible to mix as much as six inches of
sand with the pulverized clay surface at one operation, but the
chances are that the mixing will not be uniform.
In both of the above cases it will require about one-third as
much clay as sand. The amount will vary with individual cases
and must be determined to suit local conditions.
Regular use of the grader and planer will improve the sur-
face of a sand-clay road and keep it in excellent condition for
light traffic.
Cinders, Cinders and coarse ashes may also be used with
fair results on a clay soil. The use of cinders as a surface for
clay roads is rapidly growing around the industrial districts of
some eastern states. Very good results have been obtained
where the cinders were carefully selected, rolled in place and
surface treated with asphaltic oil or refined tar. The best cinders
are obtained from large industrial works and are prepared by
passing over screens to eliminate the fine ashes. If this superior
quality of material is not available an improvement in the clay
surface of the road will be effected by using straight run cinders.
In addition to their use as a surface material cinders are also
valuable as a base for gravel and macadam roads. They can
usually be obtained at little cost other than the labor of hauling
and placing.
Shale. Shale is found in some localities in southern Indiana.
This material varies in quality from a hard clay to a soft stone.
The former is but little better than common clay and probably
not worth the labor of hauling and placing on the road. Some
of the harder varieties give good results for light traffic when
placed on a well shaped sub-grade.
The cost of these improvements, in addition to the initial
shaping of the sub-grade and side ditches will vary from $500
to $2,000 per mile, or a total cost per mile for all work and ma-
terials of $800 to $5,000.
CHAPTER V
MAINTENANCE OF SAND-CLAY, CINDER AND SHALE
ROADS
These roads, constructed of inferior materials, require fre-
quent attention to keep them in good condition and should be
maintained in a somewhat similar manner to earth roads. There-
fore the maximum intensity of maintenance .will occur in the
spring. They are easily softened by water and consequently re-
quire frequent use of the grader, drag or planer. New material
of the same character as that in the road surface should be added
where necessary after the road has been softened by rain. These
surfaces require less maintenance work than an earth road and
carry traffic much better. They can be maintained in good
condition for a cost of $75 to $150 per mile per year for light
traffic.
CHAPTER VI
GRAVEL ROAD CONSTRUCTION
A decade or more ago before the extensive use of the auto-
mobile and motor truck Indiana was noted for its excellent
gravel pikes which formed the greatest mileage of improved
roads. Motor vehicles are particularly destructive to the roads.
Fifteen years ago 85 to 95 percent of the vehicles were horse
drawn while at the present time 90 to 95 per cent are motor
powered. The total number of vehicles passing over the roads
has increased many fold. As a consequence of these changed
conditions the roads have been badly worn and in some cases
nearly destroyed. Improved standards of construction are there-
fore necessary to meet the changed traffic conditions.
Fig. 18. Washed gravel for road construction.
Well built gravel roads will carry satisfactorily a heavy traf-
fic of horse drawn vehicles, a medium traffic of pleasure automo-
biles and a light traffic of trucks. Two hundred to five hundred
vehicles per day can be carried economically under favorable
conditions.
An ideal gravel for road building should be well graded,
hard, tough and should possess good bonding qualities. Gravel
having these qualities in a large degree is found widely distrib-
uted over the northern two-thirds of the state. It is obtained
from glacial deposit banks and from the beds of streams.
There should be from 10 to 25 percent of bonding material
such as clay in the gravel. River or washed gravels do not,
as a rule, contain sufficient bonding material and it may there-
fore be necessary to add some clay to such gravel. The clay
should be spread on top and harrowed into the gravel after it
has been spread on the road. A better bonding material is lime-
stone screenings.
Washed and screened gravel can be used successfully on a
clay sub-grade. After a short time the clay will work up into the
gravel and act as a binder. Washed gravel, however, should
not be placed on a sandy sub-grade. The two readily mix under
traffic but do not bind.
All large rocks should be removed from the gravel by screen-
ing if necessary. The maximum size will vary with the char-
acter of the material, but should not be larger than will pass a
2^2 or 3 inch circular mesh screen. Pebbles in the wearing sur-
face should not exceed a diameter of 1^ inches. The maximum
size of particles may be larger when the gravel is well graded
from coarse to fine. In all cases the largest pebbles used should
constitute a fair proportion of the material. This will give a
more stable road since the larger particles are not so easily dis-
placed by traffic. If there is a large percentage of the oversize
pebbles not passing the maximum screen, it may be economical
to put them through a crusher. The crusher product is then
mixed with the screened gravel giving a superior product.
There are two general methods of construction, the feather
edge and the trench. In both cases the sub-grade should be
properly graded and drained as explained in Chapter II.
The feather edge method is the older and the one most
commonly used. The gravel is dumped in the center of the sub-
grade and is then spread and crowned by the grader or is flat-
tened out under traffic. With this type of construction the outer
edges of the gravel surface are too thin to carry the vehicles in
wet weather. As a result the edges soon become badly rutted.
The road will also have too heavy a crown.
23
A better method of construction is by trenching. On a flat
subgrade or on one that has not been improved the trench may
be formed by plowing the center of the road and moving the
loose earth to each side by a grader. On an old road that has
some crown, it is advisable to form shoulders by pulling the
earth in from the side ditches with a grader. Following the
completion of the trench, gravel may be placed as previously
indicated.
Fig. 19. A poorly constructed gravel road.
Fig. 20. A good gravel road.
The gravel should be placed in layers of not more than 4 to
6 inches in thickness with the larger pebbles and the coarse gravel
confined to the bottom layer. The top layer should be well
graded and should not contain any oversize pebbles. Each layer
should be compacted separately. While it is not necessary to
roll the gravel it is desirable if heavy traffic is to be turned on
the road immediately after construction. Loose, dry gravel is
objectionable to traffic and if the material is not well graded the
large pebbles will work to the top. Rolling with about a ten ton
roller hastens the consolidation of the gravel. If the gravel is
very dry it should be sprinkled during the rolling. The com-
pleted road should have a crown of not to exceed y 2 inch per
foot which should be carried across the shoulders to the ditch
line.
Modern traffic with its heavy, fast moving loads requires a
heavier surface than was formerly necessary. Not less than 8
inches of gravel should be used and 10 to 12 inches may be nec-
essary on an inferior subgrade or for very heavy traffic. These
values may be reduced one-third on the edges of the roadway.
To provide for shrinkage the thickness of loose gravel should
be approximately 20 percent greater than the compacted thick-
ness.
" '
Figr. 21. Poor drainage and insufficient depth of surface material caused this
gravel road to break up.
A small mileage of roads has been constructed in the fol-
lowing manner. The large oversize pebbles and small boulders
are placed on the subgrade to a depth of 6 to 12 inches, the voids
between the larger stones being filled with smaller ones until a
fairly uniform surface is secured. This is then rolled after which
the gravel is added as described above. Such a road should be
somewhat superior to the common type of gravel road.
Minnesota and Iowa have developed the following method
of constructing gravel roads which gives very satisfactory re-
sults when properly applied. The same method can also be
25
used when applying maintenance gravel. The gravel is deposited
on the shoulders of the road and then carried to the surface with
a blade grader. As traffic compacts the loose material, additional
amounts are added until the entire quantity has been used. An
advantage of this method is the small amount of loose material
on the road at any time. There is also no necessity of a roller
or other costly equipment. The method probably originated in
Minnesota where the material was hauled and placed along the
road during the winter for the sake of cheaper haul costs at a
time when labor and teams were available.
The cost of a gravel road varies greatly with the cost of
labor, material and other conditions. Roads similar to those de-
scribed could probably be constructed nearly anywhere in Indiana
for $7,000 to $10,000 per mile.
CHAPTER VII
GRAVEL ROAD MAINTENANCE
Under favorable conditions a gravel road will be smooth,
resilient, comfortable to travel and will afford good traction to
all kinds of vehicles, but in order to preserve these conditions
systematic maintenance is necessary.
During the first few months after construction, the road
should be carefully maintained. Ruts, holes, wheel tracks and
weak spots should have new material added which should be of
the same kind as that in the road. It should only be added after
a rain or when the road is wet as it will not bond with the old
gravel when dry. During the period of seasoning the drag,
planer and grader should be used to bring the surface to a uni-
form, smooth contour.
The characteristic failure of an old gravel road under high
speed traffic is a pitting of the surface. This is caused by the
loosening of the surface particles and the pulverizing of the bind-
ing material under traffic. The fine binding material is then
picked up by the air currents and suction caused by the moving
vehicles and the greater part of it is blown away from the road.
As a result the pebbles have nothing to hold them together and
are easily thrown out by the wheels of the vehicles.
A road planer is one of the best pieces of machinery to be
used for the constant maintenance of a gravel road. By its use
the road can be kept entirely free from waves or large irregu-
larities. With heavy traffic and several weeks of dry weather
some pitting of the surface can not be avoided. A light dressing
of fine gravel with a minimum of binding material is very useful
in maintenance. This material is carried to the low spots by the
planer and gradually becomes consolidated with the road surface
26
When the road becomes thickly and deeply pitted a partial
reconstruction is the only remedy. The surface should be scari-
fied to a depth of not more than two or three inches; it should
then be shaped with the blade grader and a few inches of new
material should be added.
Fig. 22. Dangerous point on road caused by short culvert.
Fig. 23. Safe road with extended culvert.
Highway officials are often compelled to improve and main-
tain old gravel roads that are too narrow or too highly crowned
for present traffic. The first step is the preparation of the shoul-
ders with a blade grader by cutting away the sod on both sides
of the traveled way. New gravel may then be added on both
27
sides of the center of the road, leaving the hard surface at the
center to carry vehicles while the ne,w material is gradually being
compacted. This method has been used successfully on many of
the state roads of Indiana.
The cost of maintenance of a gravel road varies from $100
to $500 per mile per year for average traffic, but on heavily
traveled trunk lines it may reach the sum of two or three thous-
and dollars. The latter values are two or three times a desirable
maximum and indicate the annual maintenance of the road
amounts to a partial reconstruction. Under these conditions the
road is used beyond its economical capacity and it should be
replaced with one of higher type.
CHAPTER VIII
MACADAM ROAD CONSTRUCTION
A stone or macadam road was one of the first types to be
developed in America. In the early part of the last century the
travel between Boston, New York, Baltimore, Washington and
Philadelphia was principally by stage coach. The old stage
routes were hoof deep with dust when dry and hub deep with
mud when wet. In order to improve traveling conditions broken
stone was dumped on the surface. The result was not entirely
satisfactory, but was a material improvement over previous con-
ditions. Travel was lifted out of the mud and dust which was
the chief object of the improvement. As a result of this early
work, road building was stimulated and for over one hundred
years the mileage of stone and macadam roads has steadily in-
creased. Macadam roads are suitable for about the same char-
acter of traffic as gravel roads.
There are two types of stone roads, the unbound and the
water-bound macadam. In the first type the broken stone is
spread on the earth sub-grade and is then compacted by the
action of the weather and vehicles. In the second type the
broken stone and screenings are cemented into a solid mass by
means of water and rolling.
Limestone is the principal material used in the construction
of stone or macadam roads although granite, trap, slag and some
other materials are used to a lesser extent. Limestone is widely
distributed in a suitable quality for road work. The stone should
be well graded in sizes between y\ inch and 3 inches, although
some late specifications allow a maximum size passing a 3^
inch circular mesh screen. The stone dust and all particles of
stone smaller than l /\. or y inch in diameter should be removed
by screening at the crusher. The latter product is commonly
termed screenings.
Because of the uniformity of quality and grading the prod-
uct of some commercial crusher is desirable although this may
28
not be practicable on account of excessive transportation costs.
In that event if a good local ledge of rock or a supply of field
boulders in sufficient quantity is available a portable crushing
and screening plant can be installed. These plants will produce
50 to 125 tons of crushed stone per day while a large commercial
plant may turn out as much as 1000 tons per day. Before de-
veloping a local supply the stone should be submitted to a repu-
table laboratory to determine its fitness for use. Caution should
be used in the installation of a portable plant to crush field
boulders, as they may be so hard as to be beyond the capacity
of any but the largest size crushers.
All rules for grading, alignment, drainage and construction
of sub-grade as detailed in previous chapters apply to macadam
road construction. The sub-grade may or may not be trenched.
The trench method is of course the superior method.
The unbound macadam. road is constructed by placing the
crushed stone on the previously prepared sub-grade. It is usually
roughly spread to the desired thickness. Screenings are then
spread over the top to bind the material together. A greater
quantity of screenings is required than in a water-bound mac-
adam. Crusher run material containing the screenings is some-
times used. The road is then left to the action of weather and
traffic. Such a road may after a time of seasoning give good
service for light traffic but it usually does not wear evenly. The
chief argument for this type of construction is low first cost due
to the absence of sprinkling and rolling. While the first cost will
be less than a water-bound macadam, a large amount of mainte-
nance is necessary to put it in good condition after construction
and in the end the results will seldom be entirely satisfactory.
A water-bound macadam road should be at least 8 inches
thick to carry heavy traffic. In some cases 10 inches or more
will be economical and necessary. In computing quantities about
20 per cent should be allowed for shrinkage during rolling and
for the stone that will be rolled into the sub-grade. There will
be required in addition 10 to 15 per cent of screenings. If the
sub-grade is flat the edges of the road may be thinner than the
center by the total amount of the crown slope which should not
exceed ]/2 inch per foot.
'/*/'
VI
k- J"-l #
Fig. 24. Suggested cross-section of a macadam road.
It is necessary that the stone be confined between solid
shoulders so that it will be thoroughly compacted by the roller.
29
The stone may be placed on a flat sub-grade but a light crown
in the base gives a superior condition as suface water is more
easily eliminated. The stone should never be placed until the
base has been thoroughly weather seasoned or rolled with a
heavy roller to remove all shrinkage.
Some of the eastern states build water-bound macadam
roads only on top of Telford bases. This consists of large irreg-
ular blocks of stone laid by hand on the sub-grade, the open-
ings being filled with spalls and small stones and the whole
rolled. This makes a stronger road but also adds materially to
the cost.
After the base has been prepared the stone is dumped from
wagons or trucks and evenly spread to the desired loose depth.
Not over 5 to 6 inches in depth of loose stone should be placed
at one time as more cannot be compacted under the roller. A
simple way to control the depth is by means of wood blocks of
the desired thickness placed on the base. These are moved for-
ward as the work progresses. Delivery should be made in such
a manner that the vehicles will not pass over the freshly spread
stone.
A 10 or 15 ton roller should be used to roll the stone. Roll-
ing ceases when the stone no longer shifts under the roller or
when it begins to crush. Another layer should then be applied
and rolled in a similar manner. The shoulders should also be
rolled with this course so that the stone and shoulder will pre-
sent an unbroken surface.
Fig:. 25. Sprinkling: macadam prior to last rolling.
The last step is to apply and roll the screenings into the
surface. They should be applied by casting from a shovel. To
insure an even distribution the loose screenings may be swept
30
into the surface. The surface is then sprinkled and this followed
with the roller. The rolling is continued adding more screenings
as they work into the spaces between the stone and sprinkling
until completed. The rolling should be stopped when a light
wave of mortar forms as the roller passes over the surface. No
more screenings should be used than is necessary to bind the
surface, since the most even wear occurs when the traffic is
carried on the larger particles of stone.
The road may now be closed to traffic for two or three days
until the mortar has time to set up ; although there is no particu-
lar objection to opening it to traffic immediately. It should be
carefully watched for a few weeks as some spongy spots will
appear under traffic. Screenings should be placed on these spots
and broomed into the surface. They should then be sprinkled
and rolled. A road of this kind well constructed will carry 300
to 800 vehicles per day with proper maintenance, providing not
more than fifty to seventy-five per cent are motor vehicles. For
motor traffic heavier than seventy-five per cent the road should
have a bituminous carpet.
Fig 1 . 26. A properly shaped and
<l:im road.
In 1920 an eastern state rebuilt 18 foot water-bound maca-
dam surfaces 5 inches thick on Telford bases for $10,000 per
mile. This included the cost of cleaning off the old worn ma-
cadam surface which was used for widening and building up
narrow shoulders. It is estimated that the present cost of an
8 inch water-bound macadam road in Indiana would be $8,000
to $15,000 per mile.
31
CHAPTER IX
MACADAM ROAD MAINTENANCE
When a macadam road is in a perfect condition the sensa-
tion of traveling over it is very pleasant. It also offers small
resistance to travel ranking close to some hard surfaced types
in this factor. Unfortunately these high qualities are rapidly
destroyed under fast moving automobile traffic. The fine stone
dust that acts as a binder of the larger particles is picked up by
the traffic and blown away. The surface presents a coarse,
rough appearance and finally becomes deeply pitted similar to
an old gravel road.
Fig. 27. Crushed stone for maintenance along highway.
Here again the methods of maintenance are similar to those
of a gravel road. A mulch of fine stone screenings on the sur-
face is useful to supply the deficiencies and fill small holes.
Eventually under constant and heavy traffic this will not be
sufficient and pot holes will appear. If the pitting is not too
deep or extensive about two inches of clean, coarse sand or fine
gravel may be added. When the irregularities become too great
nothing remains to be done but a general scarifying and reshap-
ing of the surface together with the addition of new material.
This should be followed by rolling.
The addition of a gravel wearing surface to a crushed stone
base is finding increased favor in some localities for secondary
32
roads. The combination gives the stability of crushed stone for
the base with the wearing qualities of gravel for the surface.
Fig. 28. Spreading: a thin covering: of new material with truck.
The cost of maintenance of a macadam road will vary with
the amount of traffic, climate and other conditions. A rather
large investment is involved in the first cost of a macadam road
and it is therefore economy to conserve this investment by care-
ful maintenance. When the maintenance charge becomes too
large it will be economical to give the road a surface treatment
of bituminous material after which it is maintained as a bitumin-
ous road.
CHAPTER X
DUST PREVENTION
Water, oils, tars and other substances are applied to the sur-
faces of earth, gravel and macadam roads for the purpose of re-
ducing or preventing dust and lessening the maintenance ex-
pense by rendering the surface more stable.
Dust is formed on a road by disintegration or loosening of
the surface, by earth from the shoulders, by material carried by
the wheels of vehicles from other roads, by the droppings of
horses and by other causes. Dust is not only disagreeable to
the traveler but is also a menace to health as many of the respira-
tory diseases are directly traceable to dust arising from the roads
and streets. Dust injures the fine finish of vehicles, increases
wear of bearings and is a cause of motor troubles. It is carried
away by the wind and may result in the ultimate failure of the
road. Because of the conditions enumerated a reasonable ex-
penditure of money for its suppression is true economy.
33
Water is used largely in the cities to allay the dust but it
is never entirely satisfactory. In {Jie summer frequent applica-
tion is necessary, and if too much is used a sloppy surface will
result. In the case of rural roads the cost of application is pro-
hibitive, i
Calcium chloride may be used in place of water with im-
proved results. This was formerly applied, after dissolving in
water, by a common sprinkling wagon. It is now applied more
successfully in the dry form. The dry chloride is prepared in an
improved flake which is easily spread by a grain or fertilizer
drill. The virtue of calcium chloride lies in its affinity for water.
Moisture is absorbed from the atmosphere at night thereby
keeping the road damp during the day. Two applications of the
chloride are sufficient in an average season although in excep-
tional cases more will be necessary. The first application will
require 1 to \ l / 2 pounds per square yard. This should be followed
a few weeks later by half that quantity. The cost will vary from
2 to 4 cents per square yard of surface per season.
The advantages of calcium chloride are that it is odorless,
is not injurious to the hoofs of animals and does not stick to the
wheels of vehicles. A road treated with it can be maintained in
the usual manner with drag, planer or scraper.
Fig-. 29. Oiling a macadam surface to prevent dust.
Tars and oils have been used more largely for dust suppres-
sion than other substances. For this purpose the lighter and less
viscous grades of oils and tars are used. They may be applied
either hot or cold from gravity or pressure distributors. The
best results are generally obtained when the material is applied
hot with a pressure distributor. The cost of this method is a
34
little greater than gravity distribution unless there is a large
amount of surface to be covered. For gravel and macadam roads
the material should be somewhat heavier than is suitable for
earth surfaces. From % to */> gallon per square yard is applied
but to obtain the best results not more than y 2 gallon should be
applied at one time. As a rule tars have not been entirely satis-
factory for earth road treatment and their use for this purpose
is not recommended.
The oil or tar should be of a quality that will harden or "set
up" within 24 to 48 hours after application. Some oils act as a
lubricant with a consequent tendency to disintegrate the road
surface. It is therefore important that only good grades of
asphaltic or semi-asphaltic oils or suitable tars should be used.
Where oils are used the asphaltic content will vary from 30 to
65 per cent.
Suitable preparation of the road is as essential as good oil or
tar. The surface, should be carefully shaped. All holes or de-
pressions should be filled with new material similar to that in
the original surface. This should be tamped or rolled. The road
should not be oiled immediately but, if possible, traffic should
pass over it for at least one week. A longer period would be
preferable. The traffic will find the weak spots which should
again be repaired. The object of this careful preparation is to
secure a smooth surface with a uniform texture. Just prior to
oiling, the dust should be brushed from the surface. This can be
accomplished in the quickest and most economical manner with
a street sweeper or power broom. The sweeping should be done
with just sufficient pressure to remove the dust. If too much
pressure is used the binder in the road suface will be loosened
with resulting damage to the surface. In the event that a
sweeper is not available the oiling should be done following a
heavy rain. No oil should be applied, however, until the surface
is completely dry. In applying the oil one-half of the road should
be treated at a time. Traffic should be kept off the fresh oil from
24 to 48 hours after which the other half of road may be treated
in like manner. Any excess of oil should be covered and ab-
sorbed with a small amount of coarse sand or stone grit. The
total cost of labor and material will vary from three to twelve
cents per square yard per season.
35
CHAPTER XI
BITUMINOUS CARPETS
Prior to the application of a bituminous carpet the road sur-
face should be repaired and put in the best possible condition
as just described for oiling. It is even more essential that the
dust should be removed. Bituminous carpets are not applied to
earth roads. They are placed with good success on macadam
surfaces but with only partial success on gravel surfaces. The
latter surfaces will break up to some extent in the spring and
must be reshaped and retreated. Highway engineers are work-
ing on the problem of applying bituminous carpets to gravel
surfaces and it is probable that their efforts will be successful in
the near future. In Maine fairly good results have been attained
by treating the gravel surfaces with refined tar. In general the
best results have been secured where bituminous carpets have
been applied on macadam roads having a minimum of fine bind-
ing material.
Fig. 80. Spreading cover material on a bituminous carpet.
The hot bitumen should be applied to the clean, dry surface
with a pressure distributor, and should be covered immediately
with a light dressing of pea gravel or stone chips. The covering
material should be hard and tough so that it will not be easily
broken or disintegrated. Pea gravel well graded from l /\. inch to
^8 inch is desirable while the stone chips may vary from T 4 to
Y^ inch. Under average conditions, after the first season, about
l /4 gallon of bitumen and 15 pounds of pea gravel or 20 pounds
of stone chips will be required per square yard of surface. At
present prices of labor and materials the cost would be 8 to 14
cents per square yard per year.
36
A bituminous carpet when properly applied gives good trac-
tion, is pleasing to the eye, is waterproof, protects the material
underneath from wear, is quiet and dustless. We therefore find
that it has many of the excellent qualities of the best grade of
hard surface pavements.
Fig:. 31. A bituminous surface tlmt has been neglected.
Fig. 32. A good bituminous surface highway.
Pennsylvania, New York, Connecticut, Rhode Island and
other eastern states have thousands of miles of old macadam
roads with bituminous carpet surfaces that carry successfully
500 to 2000 vehicles per 24 hours.
PURDUE UNIVERSITY
Lafayette, Indiana
A collegiate institution founded upon an act of Congress of
July 2, 1862, maintained by appropriations from the State of
Indiana and the United States, aided by numerous private and
public gifts and named in honor of John Purdue, a citizen of La-
fayette; offers instruction in both undergraduate and graduate
courses in Engineering, Science, Agriculture and Pharmacy.
The institution possesses superior resources for conducting
the courses of instruction, viz :
An instructional corps of over two hundred persons.
An estate of over one thousand acres.
Twenty-six principal buildings.
Extensive laboratories of Chemistry, Physics, Botany, Zo-
ology* Bacteriology, Electrical Engineering, Steam Engineering,
Gas Engineering, Locomotive Engineering, Hydraulics, Mater-
ials Testing, Practical Mechanics, Pharmacy, Soil Physics, Dairy-
ing, Horticulture, Veterinary Science, Animal Industry and Ex-
perimental Fields and Orchards.
An equipment of laboratory apparatus and materials in all
departments of unusual extent and varied character.
RE'
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